A study is proposed for the purpose of examining the effects of reduced blood and oxygen supply on the function and metabolism of the mammalian heart. Investigations will make use of diving seals and dogs. Recent studies in this and other laboratories have shown that the adaptations of seals and other marine mammals to diving asphyxia are specific and highly developed examples of general vertebrate adaptations to asphyxia. Specific research projects will be: (1) further studies of adaptations of seal heart to asphyxial hypoxia of diving, including: myocardial metabolism, determinant of oxygen consumption, development of collateral circulation in response to ischemia and mitochondrial function in hypoxic and ischemic myocardium; (2) simulation of the diving seal's greatly reduced cardiac oxygen consumption as a potential therapeutic intervention in myocardial ischemia, the treatment technique to be tested in dogs in which experimental coronary occlusion has been induced. The methods will include the use of radioactive-labeled microspheres for determination of myocardial blood flow distribution, catheter-tip pressure transducers for measurement of ventricular pressures, implanted ultrasonic microcrystals for measurement of myocardial dimension changes and wall thicknesses, catheterization of arteries and the coronary sinus for obtaining arterio-venous differences of metabolic substrates in the myocardium and mitochondrial extracts prepared from fresh tissues.